Blender API documentation - where are the constructors?
I see, in that api_doc there is info about class functions but not how you can construct that class.

Go into python console and type the class name, follow with ( and hit CtrlSpace. It will hint what it wants:



It's however not the only way to create (get) that object. Numerous other functions or classes can return Euler:

Quaternion.to_euler()
Matrix.to_euler()


And you can get those also in many ways.

Btw. always use the up-to-date docs version: https://www.blender.org/api/blender_python_api_2_77_0/mathutils.html

This new version has the constructor infos there.